1. Technical Field
This invention generally relates to methods for determining the presence of appendicitis in human beings. More specifically, it is concerned with methods for determining the presence of appendicitis based upon chemical analysis of the urine of human beings suspected of having appendicitis. The significance of this invention follows from the fact that the diagnosis of appendicitis very often challenges a physician's ability to differentiate this disease from other abdominal or pelvic disorders such as abdominal aortic aneurysm, pelvic inflammatory disease, ectopic pregnancy, ruptured or perforated viscus, gastro-intestinal bleeding, hemorrhagic pancreatitis, perforated diverticulum, ovarian abscess, Crohn's disease, mesenteric adenitis intestinal obstruction, gastroenteritis, diverticulitis, ovarian cyst and tubo-ovarian pathology.
That is to say that were it not for the fact that such diseases often simulate appendicitis, and the fact that a fully developed picture is seldom available to the physician, a diagnosis of appendicitis would be relatively straightforward: confirmation of periumbilical pain of less than 72 hours duration, migration of such pain to the right lower quadrant in a patient with a temperature of 99.5.degree. to 101.3.degree. F., evidence of abdominal tenderness, abdominal rigidity, a right-lower-quadrant abdominal mass and the presence of a mass on rectal examination. The diagnostic indicators described above, when found, are representative for patients later described in this patent disclosure as "suspected of having appendicitis". In many respects, negative predictors of appendicitis are often more helpful in excluding appendicitis from a diagnosis. The most commonly employed negative predictors include: symptoms lasting more than 72 hours, pain at locations other then those noted above, temperature below 99.5.degree. or above 101.3.degree. F. and the absence of anorexia.
Unfortunately, neither leukocyte counts nor roentgenograms are sensitive or specific to appendicitis. Moreover, no reliable chemical tests for the detection of appendicitis have been heretofore developed. Hence, diagnosis of appendicitis is made almost solely on those clinical grounds noted above. Consequently, a large number of patients are taken to the operating room for explorative operations, with an average false positive experience of about 20%. This rather high false positive experience is tolerated because prompt action is needed to prevent this acute disease, curable by appendectomy, from advancing to one complicated by perforation, peritonitis, long-term sequelae, and even death.
In its most fundamental aspect, the practice of this invention enables the physician to correlate the presence of certain threshold concentration levels of .sigma.-hydroxyhippuric acid with the presence of a particular disease state, namely, appendicitis. Applicant's findings are important because .sigma.-hydroxyhippuric acid is normally formed in lesser concentrations by the body. Such formation is believed to occur chiefly through conjugation of orthohydroxybenzoic acid (salicylic acid) and glycine. The enzyme that catalyzes the reaction has been named glycine N-acylase and, as its name implies, its action leads to the formation of a number of different glycine conjugates. Hence, .sigma.-hydroxyhippuric acid is a normal constituent of the urine in man, as well as in the urine of other animals such as the horse, and the dog. It is also found in cow's milk. However, those skilled in this art will appreciate that these observations, in and of themselves, permit no conclusions regarding the source of the compound in the urine, i.e., whether it was of dietary origin completely, or whether the .sigma.-hydroxyhippuric acid was partly or entirely endogenous in origin. For example, some basic biochemical studies have shown that orthohydroxybenzoic acid may be formed via the acetate-malonate pathway as well as by the shikimic acid pathway. It has also been suggested that the compound may also be derived from tryptophan.
To a large extent, the urinary excretion of .sigma.-hydroxyhippuric acid has been studied through the administration of salicylate and/or through the administration of .sigma.-hydroxyhippuric acid itself. However, there is a much more limited body of knowledge regarding the physiologic and pathologic implications of excessive formation of .sigma.-hydroxyhippuric acid as a manifestation of disease and distorted metabolic processes. For example it is known that .sigma.-hydroxy-hippuric acid is both filtered 10 and secreted by the kidneys, secretion occurring, at least in the dog, when high blood levels occur. It also appears to accumulate in the cortex of rabbit kidney slices. Hypoxia seems to diminish this accumulation. When taken by mouth by human beings, .sigma.-hydroxyhippuric acid is known to change, at least in part, back to salicylate. In the dog it depresses the excretion of para-amino-hippurate.
The presence or absence of .sigma.-hydroxyhippuric acid in the urine of humans has been associated with certain specific disease states. These associations are well summarized in the literature, (see, generally, Clinical Pharmacology & Therapeutics 15(2):111-117, 1974). For example, such literature teaches that the presence of fever conditions generally tend to decrease the formation of .sigma.-hydroxyhippuric acid. Liver disease, however, generally does not produce any change in excretion of .sigma.-hydroxyhippuric acid. On the other hand musculoskeletal trauma and abdominal operations are thought to increase the output of .sigma.-hydroxyhippuric acid. Increased excretion of .sigma.-hydroxyhippuric acid also has been noted in patients with anemia and chronic traumatic musculoskeletal trauma. It also has been noted that levodopa and methyl dopa may increase excretion of .sigma.-hydroxyhippuric acid. Uremic patients show increased levels in serum and dialysis fluid. Some of the more detailed and documented observations thus far made in the literature concerning .sigma.-hydroxyhippuric acid/disease relationships are as follows:
Fever PA0 Trauma PA0 Anemia of Trauma PA0 Liver Diseases PA0 Hypertension PA0 Levodopa and Methyldopa PA0 Down's Syndrome PA0 Uremia PA0 Pheochromocytoma
It has been found that formation of .sigma.-hydroxyhippuric acid from salicylic acid is much decreased in febrile patients (Kapp, E. M., and Coburn, A. F.: Urinary metabolites of sodium salicylate. J. Biol. Chem., 145:549-565, 1942).
Abdominal operations have been found to be followed by increased urinary output of .sigma.-hydroxyhippuric acid as well as hippuric acid (Szumiel, I., Chmielewska, I., and Manicki, J.: N-substituted peptides in urine in the postoperative period, Bull. Acad. Pol. Sci. (Biol) 13; 565-567, 1965). Again, the urines of patients with severe musculoskeletal trauma were discovered to contain increased amounts of this material from endogenous sources. This increase was particularly striking in patients with poor wound healing. In this connection it is interesting to note that salicylates are generally thought to retard wound healing. However, there are no corresponding data on any such possible effect from .sigma.a-hydroxyhippuric acid. However, the existence of large amounts of .sigma.-hydroxyhippuric acid suggests the presence of its precursor, salicylic acid. It also had been shown that salicyluric acid, when administered, is partly hydrolyzed to salicylate.
The finding of increased endogenous production of .sigma.-hydroxyhippuric acid in patients after trauma also suggested that increased activity of the tyrosine-dopa-catecholamine pathway may be measured by studying the urinary excretion of the compound. In fact, this increased excretion may explain the mysterious failure of patients with severe chronic trauma to excrete increased amounts of catecholamines and valine mandelic acid ("VMA") derivatives in the urine. In effect, the compound may indicate a second alternate pathway in catecholamine metabolism (the other being the indole pathway).
Patients with chronic traumatic musculoskeletal lesions have an agenerative-hemolytic anemia that has not yet been fully characterized. Among other things, such patients are known to lose excessive amounts of iron and copper in their urine, a fact of great interest with respect to their increased output of .sigma.-hydroxyhippuric acid, a substance known to chelate metals. However these patients are also known to excrete other metal-chelating compounds in their urine.
The decreased hippuric acid formation and excretion that occur in patients with extensive parenchymatous liver disease has naturally led to a study of .sigma.-hydroxyhippuric acid formation and excretion in such patients. The amount of the compound excreted after the ingestion of aspirin by such patients is normal or low. In dogs with portocaval shunts, a decreased amount of salicyluric acid is excreted in the urine.
The excretion of .sigma.-hydroxyhippuric acid is usually normal in patients with hypertension but may be slightly increased or decreased in some of them.
Giving methyldopa to female albino rats caused increased urinary output of .sigma.-hydroxyhippuric acid; however, administration of the drug in therapeutic doses to a woman and to a man did not have this effect. It should also be noted that in other studies on urine samples taken from patients who were receiving levodopa for parkinsonism, a majority were found to contain large amounts of compounds with the chromatographic and fluorescence properties of .sigma.-hydroxyhippuric acid and related compounds (Altschule, M.D., and Hegedus, Z. L., .sigma.-hydroxyhippuric (salicyluric) acid--its physiologic and clinical 10 significance; Clinical Pharmacology and Therapeutics, 15: (2) 111-117, 1974).
Children with Down's syndrome have an abnormality of salicylate metabolism. Following the ingestion of aspirin there is an abnormally large amount of it bound in the red blood cells, and a much lower concentration in the plasma. Their urinary output of .sigma.-hydroxyhippuric acid is abnormally low after they ingest aspirin.
Increased amounts of hippuric acid are found in the body fluids of patients with renal insufficiency. Increased amounts also are found in their serum and also in their dialysis fluid. It has been postulated that its increased concentration might be responsible for some of the manifestations of uremia. Whether or not this conclusion is valid remains to be seen. However, the removal of considerable amounts of the compound via dialysis raises the interesting possibility that by binding iron, the compound carries off enough iron to explain the mysterious iron loss of dialysis.
Patients with pheochromocytoma are known to excrete large amounts of catecholamines but only normal amounts of .sigma.-hydroxyhippuric acid.
Thus, it would seem fair to say that the literature does not appear to teach or even suggest that the presence of .sigma.-hydroxyhippuric acid may be used to diagnose the presence of appendicitis. Obviously, given the fact that the diagnosis of appendicitis is now made on clinical grounds alone, and given the high false positive experience inherent in the prior art's forced reliance on clinical grounds alone, a chemical test, and especially a chemical test with both a high sensitivity and a high specificity, would be of extreme value to the diagnostician.